Congenital long QT syndrome presenting as unexplained bradycardia.

Congenital long QT syndrome (LQTS) is a genetically autosomal heterogeneous disorder of the ion channels and causes about 10% of sudden death infant syndrome in newborns. Its estimated prevalence is approximately 1 in 2500, probably underestimated because of its clinical heterogenicity. Few cases of neonatal LQTS have been reported. In 4% of them, life-threatening arrhythmic events can be the first manifestation of LQTS. The authors report two cases of neonatal LQTS with heterogeneous genetic mutations. Both manifested by bradycardia, one since fetal life. One case had serious arrhythmias during beta blocker therapeutic establishment needing a pacemaker implantation. Genetic mutations found were not the most frequently described in association with neonatal bradycardia, thus the importance of this report. Presentation with bradycardia is relatively frequent in neonatal period, thus LQTS should be actively investigated in neonates with unexplained bradycardia. Beta blocker therapy reduces QTc and avoids arrhythmic events and sudden death.